The World: Exotic Military Arts; On the Scent of Terrorists

By NICHOLAS WADE

Published: January 5, 2003

HOT on the scent of a suspected terrorist? Darpa -- the Defense Advanced Research Projects Agency -- hopes to give literal meaning to the phrase. It wants someone to develop a sniffing machine that can detect individuals by their body odor.

The idea is not as rank as it may seem. Dogs are said, at least by dog handlers, to recognize the scents of individual people. Researchers have found that mice can detect from body odor and urine how closely they are related to one another, a useful way to avoid inbreeding.

So Darpa, the grand patron of exotic military arts (not everything it does works, but it did have a hand in creating the precursor of the Internet), is soliciting ''innovative proposals to (1) determine whether genetically-determined odortypes can be used to identify specific individuals, and if so (2) to develop the science and enabling technology for detecting and identifying specific individuals by such odortypes.''

With the high-tech identification industry going into full gear with machines that recognize fingerprints and scan the iris, why is Darpa messing with something as old-fashioned as B.O.? Dr. Gary Beauchamp, director of the Monell Chemical Sense Center in Philadelphia, notes that odors can be detected through just a handful of molecules. Also, unlike sight and sound, the smells from a fugitive can linger for hours or days.

So supposing the C.I.A. had picked up an old jalabia worn by Ayman al-Zawahiri or Mullah Omar, perhaps it could waft the odors into Darpa's people sniffer and take the instrument on an interesting tour of the back country of Afghanistan or Yemen.

But before the marvelous machine can be built, a few small technical issues require attention. No one knows how dogs' noses work, so Darpa is following the clearer scientific tracks laid down by laboratory mice. Dr. Kunio Yamazaki of Monell showed long ago that inbred strains of mice can somehow -- presumably by smell -- detect mice with immune systems different from their own.

That makes good evolutionary sense -- if a mouse's paramour carries immune system genes different from his own, he will avoid the costs of inbreeding.

But what about people? Even if odor is of possible importance in people's choice of partners, as the fragrance industry urges you to believe, wouldn't regular showering and devotion to deodorants obliterate any natural body scents?

Not completely, it seems. Carole Ober, a geneticist at the University of Chicago, has studied the communal religious group known as Hutterites to see if, in the manner of Dr. Yamazaki's mice, Hutterite couples are more different, based on their immune system genes, than would be expected by chance.

Dr. Ober found this was the case, and last year reported a follow-up experiment in which Hutterite women were asked to sniff boxes containing T-shirts worn for 2 days by different Hutterite men. The men were told to avoid distracting odors like those from spiced foods, deodorants and sex. The women, who could not see the T-shirts and seemed unaware they were smelling a human odor, chose those of men whose immune systems matched those of the women's fathers, Dr. Ober reported.

So possibly people, like mice, do somehow detect each other's genetic status through smell, an assumption that is the basis of Darpa's proposal. ''The general idea is not that far-fetched or outrageous,'' said an expert on the mouse's sense of smell, Peter Mombaerts of Rockefeller University.

But to build its people-sniffer, Darpa needs to understand the mechanism of this strange sensibility, and that remains a mystery. The genes of the immune system make proteins, but they are too large to be given off as odors. So one theory is that the proteins of a person's immune system influence the copious bacteria that throng the surface of the skin. These selected bacteria would then give off a special pattern of metabolic breakdown products that serves as their host's signature odor.

Whoever devised the Darpa research proposal has given careful thought to all these nuances. Applicants must, within 15 months of research, identify the specific odors produced by the immune system, whether directly or through bacterial action. After another 15 months, any confounding smells produced by stress, diet, health and age must also be catalogued. And then applicants will have two more years to turn up on Darpa's doorstep with a person-sniffer that can ''identify target signatures with low false alarms.''

Get your proposal in by 4 p.m. sharp on Jan. 29. And some advice to Osama bin Laden: Forget the dry cleaner. You'd better just burn your old laundry.